Following close to a decade of speculation that it would do so, Apple (AAPL) has reportedly kicked off a project to use home-grown processors within Macs rather than Intel's (INTC) .

This isn't the kind of move that Apple can make overnight, and there are still a lot of unanswered questions. But Tim Cook's company has a number of reasons -- some fairly old, some much newer -- to pursue such a move.

Bloomberg's Mark Gurman, who has a pretty strong track record when it comes to Apple scoops, reports Tim Cook's company is planning to use its own processors to power Macs "as early as 2020." The project, still in its early stages, is said to be part of a broader effort to "make all of Apple's devices -- including Macs, iPhones, and iPads -- work more similarly and seamlessly together."

Naturally, Intel shares didn't take the news well: They fell 6.1% on Monday to $48.92 amid a 2.7% drop for the Nasdaq. In Tuesday's pre-market trading, shares were up 0.4%.

Reports that Apple has been thinking of developing its own Mac CPUs date back to 2012, but Monday's report is the first one from a reputable source to state Apple is planning to do it, rather than merely considering it. And even when there were no recent reports pointing to such a move, there was plenty of speculation that Apple would eventually make it, for a few reasons:

Apple's A-series system-on-chips (SoCs), used in iPhones, iPads and Apple TVs can already deliver performance that's arguably competitive with some PC CPUs in spite of having a very tight thermal envelope, due to battery life and heat considerations. While it's tough to make direct comparisons given OS, app and CPU instruction set differences, new A-series chips have outclassed some of the Intel CPUs used at the time within MacBooks for certain benchmarks. There's a good chance that Apple-designed processors that can afford to consume a little more power will hold their own against many Core i5 and i7 parts.

Though Intel has done a good job of developing powerful notebook CPUs that only sip small amounts of power when not seriously taxed -- on Tuesday, the chip giant unveiled new 8th-gen Core notebook and desktop CPUs with decent specs -- ARM-architecture processor lines such as Apple's A-series and Qualcomm's Snapdragon line are still viewed by many as having a power efficiency edge over x86-architecture CPUs such as Intel and AMD's. That's particularly true in terms of total system power consumption.

Apple has been steadily expanding the amount of chip engineering work it does. In addition to mobile SoCs, Apple now develops flash memory controllers, fingerprint sensors, Bluetooth audio processors and display timing controller chips. It also designs its own CPU and GPU cores for use within A-series SoCs, and has developed co-processors for Macs -- the T1 and T2 -- that control things such as a system's fingerprint sensor, boot process, camera and (in the case of some MacBook Pros) OLED Touch Bar.

Apple could potentially save hundreds of millions of dollars by using its own Mac processors. Many of the Core i5 and i7 CPUs used within Macs have list prices between $200 and $400 (Apple, like other big OEMs, presumably gets discounts), and the company ships close to 20 millions Macs per year. Even after accounting for R&D expenses and the cost of having a contract manufacturer (foundry) produce the chips, there's a lot of money to be saved.

On top of all that, there are a few recent developments that may have motivated Apple to plan a break with Intel:

Apple is reportedly developing a software platform that (per Bloomberg) will let developers "design a single application that works with a touchscreen or mouse and trackpad depending on whether it's running on [iOS] or on Mac hardware." Though this will be more useful/practical for some apps than others, it would bolster Apple's neverending efforts to pitch the iPad as a notebook alternative, and also allow macOS to better leverage Apple's massive iOS developer base.

But until Macs join iPhones and iPads in running on ARM-based processors, it won't be possible for the exact same apps to run on both sets of devices. At least without emulation software that yields a performance hit.

Qualcomm and Microsoft (MSFT) have teamed up to make ARM-based Windows 10 notebooks a reality. HP Inc. (HPQ) , Lenovo and Asus recently unveiled systems based on Qualcomm's Snapdragon 835 SoC (found in many high-end Android phones) that deliver 20-plus hours of battery life, provide 4G connectivity and can be instantly awoken from standby mode in a manner similar to a phone or tablet.

The systems have some limitations. Among other things, they don't support 64-bit Windows apps for now, and their reliance on emulation software to run x86-architecture apps (there aren't many ARM-based Windows apps right now) makes them unsuitable for high-end users. But their battery life and instant-wake features may have gotten Apple's attention. So might the fact that after having suggested it could do so, Intel has thus far declined to sue Qualcomm or Microsoft over their use of x86 emulation software.

Intel's once-large manufacturing process lead over Taiwan Semiconductor (TSM) and other top foundries has narrowed. As Intel rolls out its first PC CPUs based on a much-delayed 10-nanometer process later this year, TSMC is expected to start production of Apple's A12 SoC using a 7-nanometer process that many view as competitive with Intel's 10nm process. Moreover, Intel has signaled that going forward, new manufacturing processes will first be put to use within server CPU lines rather than PC CPU lines.

For all the arguments in favor of doing so, however, abandoning Intel CPUs isn't a decision that Apple can take lightly. The company will have to re-write macOS to run on ARM-based processors, as well as make sure any needed drivers are supported. It will also have to get macOS developers on board in a big way.

And for more powerful macOS systems such as MacBook and iMac Pros, creating power-efficient chips that can measure up to the Intel Core i7 and Xeon CPUs currently going inside of them will take effort. Indeed, it wouldn't be shocking if Apple initially opted to only use ARM-based processors on cheaper Macs, and stuck with Intel elsewhere.

Nonetheless, considering how much ARM-based mobile processors have evolved and the degree to which the PC industry has matured, ARM PCs increasingly feel like an idea whose time has come. That spells opportunities for Apple and Qualcomm, and gives Intel one more incentive to invest heavily in data center, automotive, graphics and IoT opportunities that lower its PC CPU dependence.